I'll bet they can grow anything that they like to eat -- with that kind of incentive, it's easy to stay focused and attentive to a project. And it's always fun to grow things you can eat right there in the garden! Plant a few different crops that mature at different stages to keep the process interesting. For instance, radishes, lettuce, and peas can all be planted early in the spring. Radishes should be ready within a month of germination; leaf lettuce soon after. Choose a pea variety that does not require support or will be happy climbing a short tomato cage, and that mature within 60 days. Purchase a cherry tomato or two to put in containers after the danger of frost has passed, and sow cucumber seeds at the same time. And I can't imagine a kids' garden without pumpkins! Choose a compact (bush) variety that matures quickly for best results.